1. Field of the Invention
The present invention relates generally to a tracking system for tracking the position of a target and a missile pursuing the target. More particularly, the present invention relates to a tracking system means for determining the dynamic positions of a target and a missile tracking the target passively by correlating multiple GPS signals and event-related data.
2. Description of the Prior Art
There is a continued pressure on the military to deliver high performance weapon systems with quantifiable performance characteristics. It is expected that these weapons systems can be procured at a cost which is comparable to presently available weapon systems. Testing, in particular flight test on a full-scale range, is a major contributor to the cost of procuring a high performance system. Any opportunity to reduce test costs and thereby save defense funds for other purchases such as weapons systems is welcomed by the military.
Conventional range testing is heavily reliant on radar and optical instrumentation to provide Time, Space, Position Information (TSPI) and Miss Distance Indication (MDI) or Vectoring Scoring (VS) data. These conventional fixed systems are expensive to procure, operate, and maintain and represent a xe2x80x9csunk costxe2x80x9d independent of usage of a range testing facility. Further, the manpower needed to operate these complex range testing facilities must be available at odd hours of the day in order to meet mission requirements, necessitating the payment of overtime to specially trained operators in many cases. Also, the mobility, positioning and coverage of range testing systems is dependent on terrain. Communications among the many operators also calls for an elaborate secure communications network to be procured, maintained and operated. Finally, the ability to conduct tests in a secure mode is also severely constrained when using a specific active emitter, such as a radar, for a specified duration and readily identifiable location. A preferred embodiment of the present invention addresses each of the above deficiencies in a cost effective, reliable, and efficient package.
The present invention overcomes some of the disadvantages of the past including those mentioned above in that it comprises a relatively in design yet highly efficient and effective tracking system for providing position information relative to a missile in flight tracking a target by correlating multiple satellite generated GPS signals and event-related data. Raw position data, generated from GPS receivers onboard a moving target and a missile tracking the target, is supplied to a ground station in a IRIG (Interrange Instrumentation Group) encrypted compatible data string. To properly correlate the data and eliminate any errors in the data, a ground station GPS receiver also collects raw position data as well as emphmeris data of all the satellites in view at the ground station. The data is processed using double difference error correction techniques for post mission real time processing and kinematic processing.
A preferred embodiment of the present invention integrates a xe2x80x9csemi-passive trackingxe2x80x9d subsystem into test range instrumentation and test vehicles to provide very accurate position information. Position data is obtained by data merged from multiple Global Positioning System (GPS) receivers with instrumentation data telemetered to the ground station.
The term xe2x80x9csemi-passive trackingxe2x80x9d is used to denote that although xe2x80x9cactivexe2x80x9d signals from GPS satellites are used, their use is not traceable to a specific test or event since anyone can use these signals at any time. Unlike radars that emit signals and track objects for a specific purpose, and thus provide a fully active signal capable of being monitored, the GPS signals are always there.
The ground station or analysis site is normally a fixed location, but can be mobile such as a vehicle, given the unique capabilities that the present invention provides. The unique integration of receivers for intercepting GPS signals with existing systems allows development of an accurate reproduction of the test event. Further, it can be accomplished inexpensively, and in a very secure mode at remote locations, if necessary, to address unique mission requirements.
Each test article such as a missile or target and its instrumentation system location is precisely known at any given moment in time, by transmitting the raw GPS data and IMU measurements in xe2x80x9creal timexe2x80x9d to an analysis site or ground station where the GPS data is differentially corrected to merge the IMU data. At the site, which also has its own GPS receiver for generating its own position data, the GPS position information is then merged with other test data thus fixing the dynamic position of all elements engaged in the test. By dynamic position is meant the location and attitude of an article correlated to a given moment in time. Even the location and attitude of one test article relative to other test articles can be obtained by post-processing of the data.
Each test articles is fitted with a GPS receiver capable of intercepting GPS signals from a satellite. These receivers are built to withstand the test environment and have unique message formatting capabilities for transmitting raw GPS measurement data to a ground station. A pre-amplifier is added to each receiver to amplify the GPS signal. The GPS signal is then input to an onboard encoder where a data validation bit is added together with a timing bit and the entire data stream is telemetered as an encrypted signal to an analysis site where data from other test articles and range instrumentation is merged.
Test data is provided to the ground station, in near real time, for input to formal evaluations of a weapon system, such as a missile, as it flies an actual test mission.